Hygrometer



H. R. BRISTOL May 15, 1934.

HYGROMETER Filed Jan. 26, 1933 INVENTOR HA m1. TON R BRISTOL BY 6 sATTORNEY Patented May 15, 1934 UNITED STATES PATENT OFFICE HYGBOMETEBApplication January 26, 1933, Serial No. 653,614

6 Claims. (CL 73-24) The invention relates to measuring apparatus, moreespecially as utilized in the determination of relative humidity.

It has for an object the provision of a. simple and rugged precisioninstrument embodying. a member of hygroscopic material whose changes inphysical dimensions are indicative of the relativehumidity conditions ofthe ambient atmosphere.

It has for a further object the provision therein of a natural fibrousorganic material possessing the required capillary structure forabsorbing the moisture to which it may be exposed, said material beingmounted for intimate contact between its fibres and the ambientatmosphere whereby response of the member is rapid and definite.

Still another object of the invention resides in the arrangement of suchmaterial in an instrument in a manner to obviate distortion or irregularbending such as warping, buckling or twisting thereof, the member beingfree to bow uniformly.

A further object of the invention is to provide a responsive element ofthis nature which shall also have suflicient strength to insure apositive indication by providing a. relatively great force when exposedto humidity changes in the ambient atmosphere.

Still another object of the invention resides in the provision of ahygrometer which shall be relativeiy' inexpensive to manufacture,eincient in operation. readily installed, and durable and reliable inservice.

In carrying out the invention, the hygroscopic member is arranged to beinitially constrained to an arched conformation as by being pivotallyattached at its opposite ends to a rigid nonhygroscopic frame or blockand arched or bowed between movable abutments provided thereon. Meansare secured to the apex of the arch for transmitting to a suitablemeasuring element the eifect of elongation or contraction of the memberunder humidity variations of the surrounding atmosphere.

her, a strip of wood is utilized, the same being relatively thin and sodisposed that its fibres lie substantially parallel to its shortestdimension. The nature of the invention, however. will best be understoodwhen described in connection with the accompanying drawing, in which:

Fig. 1 is a front elevation, with parts in vertical section, of ahygrometer embodying the invention, and with the surrounding casingremoved.

Fig. 2 is a transverse vertical section thereof As a particularlydesirable hygroscopic mem-V taken on the line 2-2, Fig. 1 of thedrawing, and looking in the direction of the arrows.

Fig. 3 is a plan view of the hygrometer.

Fig. 4 is an enlarged detail .section through the hygroscopic member andtaken on'the line 4-4, 0 Fig. 3 of the drawing.

Referring to the drawing, 10 designates a suitable plate or supportmember for the novel mechanism, and a bracket 11 secured to the face ofthis plate is designed to support a block or carrying device 12 ofnon-hygroscopic material and adapted to afford a rigid support for ahygroscopicallyresponsive element 13. The latter is arranged to bepivotally attached to opposite ends of the block 12 and in archedconformation, this being effected by mounting the opposite ends of theelement 13 in respective pivot blocks 14 and 15 which are carried bypairs of pivot screws 16 and 17, respectively, mounted in pairs of lugs18 and 19 extending upwardly from the said block. The strip 13 thereforehas a substantially frictionless hearing at the abutments thus provided,and will alter its curvature in accordance with the varying conditionsof humidity of the atmosphere surrounding it, as hereinafter set forth.

The said member 13 constituting the hygroscopically-responsive elementis composed of straight-grained wood, which has first been freed fromsap and other objectionablesubstances, as by alternately immersing thesame in a solvent and boiling, and then drying. The wood may thereafterbe subjected to a process of compression, and finally is cut across thegrain in such a manner that its natural fibres 13 are substantiallyparallel to the shortest dimension of the so strip which is of athickness not exceeding 0.05 of an' inch.

It is further desirable that the center line of the strip be parallel orperpendicular to the radius of the growth rings of the original lumber,in order that the elements of these rings may be symmetrically disposedin the finished strip and thus minimize a tendency to warp and twistwith changes in moisture content. The strip, furthermore, may beprovided with a central openin 10 20 to afford a means of connection tomeasuring means hereinafter set forth. Also, the strip is so dimensionedthat when attached to the pivot blocks as aforesaid the distance betweenthe center line of these blocks is materially g ea than the distancebetween the center line of the pivot screws designed to carry thecorresponding pivot blocks. In order to mount the strip in its bearings,it is given a curved or arched conformation until the chord of the areso formed equals the 23 is designed to cooperate with a scale 24 fixed.

to the plate 10 and graduated in values representative of the curvatureof the responsive hygroscopic element aforesaid. The bell crank may bepivotally supported by a bracket 25 secured to the block 12, as shown."

Upon being exposed to an atmosphere whose humidity it is desired todetermine, the moisture of this atmosphere will cause the fibres of the20- strip 13 to swell in a transverse sense to' a degree depending uponthe relative humidity of I the ambient atmosphere. As the fibres of thisstrip are relatively short and'exposed at both ends to such atmosphere,theitendency will be toward a rapid equalization of moisture conditionsthroughout the mass of the strip, and a proportionately quick responseto changes in atmospheric humidity is attained; At the same time, sincethe fibres are disposed perpendicularly to the width and to the lengthof the strip, the latter will not have a tendency to warp or buckle,

the resulting tendency upon changes in the mois ture content of thefibres being to produce a corresponding change in the linear dimensionof the strip. Both ends of the strip being fixed, however, with respectto their linear spacing, the longitudinal response will take the formofa change in curvature of the strip, which, in turn,

varies the location of the middle portion in a direction substantiallyperpendicular to the'chord of the arc of said strip." This movement iscommunicated through the link and bell crank aforesaid for measuringmovement'with reference to the scale 24 to aiiord therebyan indicationof the relative humidity of the atmosphere to which the strip 13' isexposed.

I claim: I

1. In a hygrometer: a rigid non-hygroscopic block, ahygroscopic memberpivotally attached at its opposite ends to the block and in archedconformation, and means rigidly secured to the hygroscopic memberintermediate its ends and adapted to transmit the effect ofelongation'and contraction of the member under humidity variations inits surrounding atmosphere.

2. In a hygrometer: a rigid non-hygroscopic block, a hygroscopic memberpivotally attached at its opposite ends to the blockand in archedconformation, and means rigidly secured to the hygroscopic membersubstantially at its apex intermediate its ends and adapted tov transmitthe effect of elongation and contraction of the member under humidityvariations in its surrounding atmosphere.

3. In a hygrometer: a rigid non-hygroscopic block, a hygroscopic memberpivotally attached at its opposite ends to the block and in archedconformation, means rigidly secured to the hygroscopic memberintermediate its ends and adapted to transmit the effect of elongationand contraction of the member under humidity variations in itssurrounding atmosphere, and measrnosphere and comprising a thin strip offibrous material flexibly secured at its opposite ends. bowed and havingits fibres lying substantially parallel totheshortest dimension 'of theelement.

5. In a hygrometer: a rigid non-hygroscopic block, a hygroscopic'memberpivotally. attached at its opposite ends to the block and in archedconformation, both sides of the strip being exposed to the surroundingatmosphere and subject to humidity variations therein whereby the stripwill elongate or contract in accordance with the variations, and meansto measure the resultant change in the longitudinal dimensions of saidstrip.

6. A hygrometer unit, comprising a base plate. a rigid non-hygroscopicblock, a bracket secur-- ing said block to the base plate,'lugsextending outwardly from the block, pivot blocks mounted in therespective lugs, a bowed hygroscopicailyresponsive element secured atits opposite ends to therespective pivot blocks, a bracket secured tothe non-hygroscopic block, a bell crank pivotally mounted on saidsecond-named bracket, a link connecting one arm of the bell crank to thehygroscopically-responsive;element, and a. scale secured to thebase'piate adapted to cooperate with the other arm of said bell crank.

HAMILTON R. BRISTOL.

